They seem to be connected through the LAN 172.16.0.0/255.255.252.0,
with private IPs 172.16.0.116 (dashen,eth0) and
172.16.1.107 (vixen,eth1).
These addresses are probably what OpenMPI is using.
Not much like a cluster, but just machines in a LAN.

Hence, I don't understand why the lack of symmetry in the
firewall protection.
Either vixen's is too loose, or dashen's is too tight, I'd risk to say.
Maybe dashen was installed later, just got whatever boilerplate firewall
that comes with RedHat, CentOS, Fedora.
If there is a gateway for this LAN somewhere with another firewall,
which is probably the case,
I'd guess it is OK to turn off dashen's firewall.

Do you have Internet access from either machine?

Vixen has yet another private IP 10.1.1.2 (eth0),
with a bit weird combination of broadcast address 192.168.255.255 (?),
and mask 255.0.0.0.
Maybe vixen is/was part of another group of machines, via this other IP,
a cluster perhaps?

What is in your ${TORQUE}/server_priv/nodes file?
IPs or names (vixen & dashen).

Are they on a DNS server or do you resolve their names/IPs
via /etc/hosts?